The invention is directed to a roll stand with backup rolls and/or work rolls for rolling sheet and strip in which the upper and lower work rolls, possibly together with the backup rolls associated therewith, can be displaced from the common vertical plane into positions in which the vertical planes passing through the roll axes of the work rolls and backup rolls intersect in that chocks supporting each roll within the housing window are displaced in pairs horizontally in opposite directions.
Systems in which the upper and lower rolls of a four-high roll stand are swiveled in pairs and in opposite directions are also known as pair cross rolling systems. By means of the crossing of the rolls and the intersecting of the roll axes, the profile of the rolling stock can be adjusted without the need to apply high work roll bending forces as is usually required. This advantageously results in an increased bearing life.
Also, systems are known in which either only the work rolls or only the backup rolls are crossed in order to adjust or influence the required profile of the rolling stock in this way.
A great variety of solutions have been proposed for adjusting (crossing) rolls. For the chocks of the work rolls and backup rolls, European Patent Application 0 525 552 A1 suggests shared sliding blocks which are interposed between the chocks and the roll housing and which have, at their sides remote of the chocks, wedge faces corresponding to vertically adjustable displacing drives with the same wedge faces. When these displacing drives are adjusted or crossed, the wedge faces which slide one on top of the other cause a horizontal displacement of the sliding blocks so that the sliding blocks adjust the laterally contacting chocks and the rolls are crossed pairwise.
This same reference also shows other adjusting drives such as hydraulic cylinders or spindles which act mechanically on the chocks and by means of which the chock are displaced horizontally for changing the roll positions within the housing window.
In another known solution (DE 195 10 694.6) for crossing rolls, the crossing of the roll pairs is carried out by means of sliding blocks constructed as U-shaped pressure pieces whose webs contact the chocks by dome-shaped outer sides and whose legs engage around both sides of the column of the roll housing. Transverse bore holes, in which cams are mounted which are arranged at the roll housing and are rotatable relative to axes parallel to the axes of the transverse bore holes, are provided for the displacement of the pressure pieces in both legs engaging around the housing column of the roll housing.
All of these known cross rolling and pair cross rolling systems are very costly and usually require special work roll bearings; the rolls or roll sets must be provided with axial locking arrangements in order to absorb the axial forces occurring because of the inclined position of the rolls caused by the system. Another disadvantage consists in that adjusting structural component parts which impede the exchange of rolls are arranged in the area of the stand guides. Eccentrics and guides entail especially elaborate production methods.
Proceeding from a prior art such as is known from DE 195 10 694.6, it is the object of the present invention to provide a simply designed roll stand with simple displacing drives and high system stability enabling roll crossing with conventional bearings.
In order to meet this object, it is suggested according to the invention that each pair of rolls formed of the upper and lower backup rolls and work rolls is received by its roll chocks in one of two casings or cassettes extending horizontally into the housing windows located on either side of the roll housing and is guided therein such that it can be vertically and/or horizontally adjusted or crossed. The cassettes can be swiveled in opposite directions about a common central vertical axis formed by upper and lower centering pin bearings provided at the housing cross girder or crosspiece and at the cassette. Each cassette is vertically supported in the area of the housing windows against the roll stand frame by articulated supports mounted on cardan joints at both ends.
The invention is also applicable when a two-high rolling mill with only two work rolls is used. In this case, it is provided according to the invention that each work roll is received by its roll chocks in one of two cassettes extending horizontally into the housing windows located on either side of the roll housing and is guided therein such that it can be vertically and/or horizontally crossed. The cassettes can be swiveled in opposite directions about a common central vertical axis formed by upper and lower centering pin bearings provided at the housing crosspiece and at the cassette. Each cassette is vertically supported in the area of the housing windows against the roll stand frame by articulated supports mounted on cardan joints at both ends.
Further, it is also possible to use the invention in roll stands in which the work rolls are fixed against swiveling and the backup rolls can be crossed. In a rolling mill of this kind, it is provided according to the invention that each backup roll is received by its roll chocks in one of two cassettes extending horizontally into the housing windows located on either side of the roll housing and is guided therein such that it can be vertically and/or horizontally crossed. The cassettes can be swiveled in opposite directions about a common central vertical axis formed by upper and lower centering pin bearings provided at the housing crosspiece and at the cassette. Each cassette is vertically supported in the area of the housing windows against the roll stand frame by articulated supports mounted on cardan joints at both ends.
The proposed construction provides a highly effective solution with very simple mechanical equipment. Complicated crossing constructions with expensive axial bearing units are done away with in that the centric centering pin bearing support safely absorbs the large axial forces occurring from the crossing of the rolls in the cassettes because the centrally arranged centering pin does not permit any axial displacement of the cassette during swiveling. The vertical support of the cassettes on movable articulated supports makes possible the swiveling movement as well as a thermal expansion of the cassette without causing stresses in the system.
By introducing the rolling pressure into the crosspieces of the roll housings via the articulated supports, no necking results at the cassettes such as is known at the roll housings in conventional rolling mills. As a result, a tighter clearance can be selected between the chock and the guide, which means an improved and more secure guiding of the rolls.
The swiveling of the cassettes with the respective rolls and pairs of rolls received therein can be carried out in accordance with a further embodiment of the invention by means of essentially horizontally acting actuators or drives which act on the roll housings on the one hand and on the respective cassette on the other hand. Mechanical synchronizing means prevent tilting of the cassette in the roll housing. The cassettes can advantageously be clamped between hydraulic cylinders arranged on both sides, which ensures that the cassettes are guided without play.
According to another preferred solution of the invention, it is provided that the cassettes can be counterbalanced hydraulically against the upper and lower articulated supports. The lower counterbalancing serves at the same time to raise the system for changing rolls and to enable displacement of the step wedges for adjusting the pass line.
In another development according to the invention, it is provided that the hydraulic cylinders for adjusting the pair of rolls that is mounted in the upper or lower cassette so as to be vertically adjustable are installed inside the cassette together with the associated servo valves and the counterbalancing and bending cylinders for the rolls. On the one hand, the rolling forces are always introduced centrally in this way and, on the other hand, installation and disassembly of the rolls is appreciably simplified.
The cassette-type solution according to the invention allows a displacement of the work rolls in axial direction and a positive and negative work roll bending. The axial displacement of the work rolls can be achieved in a simple manner according to another feature of the invention when each work roll is displaceable in axial direction by means of a two-armed lever system whose swivel point is arranged at the cassette, one of whose lever arms is connected with a drive supported at the cassette, and whose other lever arm is connected in frictional or positive engagement with the chock of the work roll.
In order to facilitate displacement and to be able to introduce displacing forces into the chocks without torque, it is provided according to another feature of the invention that the lever arm is connected with the chock by rollers which are mounted in a rotatable manner at the end of the lever and are supported at the chock.
It is considered particularly advantageous when, according to the invention, the lever arms can be swiveled away in the area of the chocks transverse to the displacing direction of the work rolls to allow the work rolls to be disassembled.
The system according to the invention which is provided in this way enables positive and negative bending and axial displaceability of the work rolls in a simple functional device with a very large adjusting range for regulating profile and flatness. Dynamic pair crossing is possible in a simple manner without the need for elaborate and expensive swivel bearings or eccentric bearings.
An embodiment example of the invention is shown in the drawing and is described in the following.